Interference cancellation with a time-sliced architecture

ABSTRACT

Example embodiments include methods of interference cancellation at NodeB receivers of baseband antenna signals including physical channels. The methods include canceling interference from a received baseband antenna signal by removing a reconstructed baseband signal from the processed received baseband antenna signal. The processed reconstructed baseband signal includes users whose physical data channel signals were successfully decoded. Methods also include removing interference from a received baseband signal to form an interference cancelled baseband signal that will be processed by the receiver. The interference cancelled baseband signal is the received baseband antenna signal minus users&#39; signal interference contributions whose demodulated physical data channel signals have a determined user symbol energy value that exceeds a threshold. Methods further include removing interference from a user&#39;s signal to be error corrected. The interference is symbol interference from an earlier successfully decoded user&#39;s symbols. The user symbol interference is determined by cross correlations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 12/379,024filed Feb. 11, 2009 now U.S. Pat. No. 8,306,164, the contents of whichare hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

A cellular communications network typically includes a variety ofcommunication nodes coupled by wireless or wired connections andaccessed through different types of communications channels. Each of thecommunication nodes includes a protocol stack that processes the datatransmitted and received over the communications' channels. Depending onthe type of communications system, the operation and configuration ofthe various communication nodes can differ and are often referred to bydifferent names. Such communications systems include, for example, aCode Division Multiple Access 2000 (CDMA2000) system and a UniversalMobile Telecommunications System (UMTS).

Third generation wireless communication protocol standards (e.g.,3GPP-UMTS, 3GPP2-CDMA2000, etc.) may employ a dedicated traffic channelin the uplink (e.g., a communication flow between a mobile station (MS)or User Equipment (UE), and a base station (BS) or NodeB). The dedicatedchannel may include a data part (e.g., a dedicated physical data channel(DPDCH) in accordance with UMTS Release 99/4 protocols, a fundamentalchannel or supplemental channel in accordance with CDMA2000 protocols,etc.) and a control part (e.g., a dedicated physical control channel(DPCCH) in accordance with UMTS Release 99/4 protocols, a pilot/powercontrol sub-channel in accordance with CDMA2000 protocols, etc.).Release 5 of 3GPP introduces High Speed Downlink Packet Access (HSDPA),which is a high-speed downlink channel that has an associated controlchannel in the uplink (HS-DPCCH).

Newer versions of these standards, for example, Release 6 of UMTSprovide for high data rate uplink channels referred to as enhanceddedicated channels (E-DCHs). An E-DCH may include an enhanced data part(e.g., an E-DCH dedicated physical data channel (E-DPDCH) in accordancewith UMTS protocols) and an enhanced control part (e.g., an E-DCHdedicated physical control channel (E-DPCCH) in accordance with UMTSprotocols).

FIG. 1 illustrates a conventional wireless communication system 100operating in accordance with UMTS protocols. Referring to FIG. 1, thewireless communication system 100 may include a number of NodeBs such asNodeBs 120, 122 and 124, each serving the communication needs of a firsttype of user 110 and a second type of user 105 in their respectivecoverage area. The first type of user 110 may be a higher data rate usersuch as a UMTS Release 6 user, referred to hereinafter as an enhanceduser. The second type of user may be a lower data rate user such as aUMTS Release 4/5 user, referred to hereinafter as a legacy user. TheNodeBs are connected to an RNC such as RNCs 130 and 132, and the RNCsare connected to a MSC/SGSN 140. The RNC handles certain call and datahandling functions, such as, autonomously managing handovers withoutinvolving MSCs and SGSNs. The MSC/SGSN 140 handles routing calls and/ordata to other elements (e.g., RNCs 130/132 and NodeBs 120/122/124) inthe network or to an external network. Further illustrated in FIG. 1 areinterfaces Uu, Iub, Iur and Iu between these elements.

An example frame for the E-DCHs (e.g., E-DPCCH and E-DPDCH) in theuplink direction may have a length of, for example, 10 milliseconds(ms). E-DCHs include E-DPDCH and E-DPCCH, which may each be codemultiplexed. FIG. 2A illustrates a conventional UMTS uplink receiver 124located at, for example, one of the NodeBs 120/122/124 of FIG. 1. Theconventional receiver 124 of FIG. 2A may receive E-DCHs included inbaseband antenna signal 280, which was front-end processed and downconverted from the received antenna RF signal in step S100. Basebandantenna signal 280 is input to DPCCH, DPDCH, High Speed Data PacketAccess (HSDPA), and E-DCH receivers, 202, 204, 206, and 208,respectively. As is well known, the DPCCH receiver 202 outputs channelestimates based on DPCCHs to receivers 204, 206, and 208.

FIG. 2B illustrates a portion 208 of a conventional E-DCH receiver, 124described in FIG. 2A, which may be implemented on an ASIC, FPGA, etc.The receiver portion 208 includes E-DPCCH-RR-CT block 200, RR-FSD-CTblock 210, E-DPCCH-DEC block 240, HARQB block 230, SSD block 250, HARQcombiner block 260, and DEC block 270.

The conventional functions of the various blocks in FIG. 2B will bebriefly discussed. To process physical control channel transmissions,E-DPCCH-RR-CT block 200 includes a rake receiver for combiningmulti-path components of the E-DPCCHs included in baseband antennasignal 280 using channel estimates 290. The thus processed user E-DPCCHtransmissions are input to decoder E-DPCCH DEC block 240, for decoding.The use of “decode” in all its various forms is intended to indicatethat decoding is attempted. The result of the attempted decoding iseither indicated as “successful” or “unsuccessful” and is noted as suchthroughout. The structure and function of rake receivers are well knownand thus will not be further described.

To process enhanced dedicated physical data channel transmissions, arake receiver in RR-FSD-CT block 210 performs first stage despreadingand then performs maximal rate combination (MRC) on the multi-pathcomponents of the E-DPDCH transmissions included in baseband antennasignal 280 using channel estimates 290. In block 210, the basebandantenna signal 280 is processed on a symbol by symbol basis, where eachsymbol is divided into equal time slices and each user is assigned asingle time slice per symbol. The duration and/or length of a symbol mayvary and may be set by network properties. For example, each DPCCHsymbol equals approximately 66.7 μsec or 256 chips and may betransmitted over a Transmission Time Interval (TTI) or frame. Forexample, common TTI for E-DCHs are, for example, 10 ms or 2 ms.

Returning back to FIG. 2B, the first stage processed E-DPDCH symbols arebuffered in HARQB block 230, which may be externally located from block205, e.g., on a different part of the board or chip, etc., or may beembedded with the other identified blocks. First despread symbols areoutput from the HARQB block 230 in TTIs for each user and input to SSDblock 250, in which the symbols are further despread, deinterleaved, andrate dematched. The second stage processed symbols for each user arecombined in HARQ combiner block 260 and finally decoded in Dec block270.

As is well known, the baseband antenna signal 280 includes multiple usersignals, each user signal including a first transmission and/or aretransmission. The retransmission results from the Dec block 270 notsuccessfully decoding a user's earlier transmission or retransmission asa result of inadequate error detection (e.g., signal to interferenceratio). If a decoder is unable to decode a user's transmission, theun-decoded transmission is discarded and a Negative Acknowledge (NACK)response is sent to the transmitter by the receiver requesting thetransmitter retransmit the user's signal. Various types of errorcorrection and decoding may be used. For example, HARQ combining anddecoding are well known processes that accomplish the above byretransmitting the user's transmission having the same data but possiblya different encoding pattern. Also well know are interleaving, ratematching, Turbo encoding, convolution coding, and CRC attachment.

As shown in FIG. 3, multi-user interference occurs when multiple usersare transmitted in the uplink in the same frequency band and at the sametime using quasi-orthogonal codes. For example, channel 300 of FIG. 3includes users 1 to N including user k. Focusing on user k as an exampleof a user signal, when user k's signal is despread by despreader 310,the resulting signal 320 includes interference from all of the otheruser signals (e.g., user N to user 1), thermal noise, non-WCDMAinterference (e.g., other sources of man-made or natural interference),and user k's signal. To reduce the effect of interference, a user'ssignal's power may be increased, but increasing a user's signal powerdoes not normally help as once one user increases his power, the otherusers follow suit. However, removing (or canceling) other users'interference has been found to enhance cell capacity.

Two well known types of interference cancellation include successiveinterference cancellation and parallel interference cancellation. FIG.4A illustrates an example of successive interference cancellation andFIG. 4B illustrates an example of parallel interference cancellation.

In FIG. 4A the strongest user signal of an incoming baseband antennasignal is decoded at step S400 and if decoded successfully, the decodeduser signal is reconstructed and subtracted at step S410 from thebaseband signal. This process is repeated for the next strongest userand is continued for a determined number of users.

In FIG. 4B, all user signals of an incoming baseband antenna signal aredetected simultaneously and coarse estimates are made for each usersignal. The coarse estimates are subtracted from the other user signalsto cancel interference. For example, in FIG. 4B two user signals aredetected simultaneously and coarse estimates for each user's signal isdetermined in Despreaders 420 and 420′. Each coarse estimated usersignal is then subtracted from the other user signals in Subtractors 430and 430′. Following the subtraction, the user signals are processthrough another Despreader 440 or 440′, Deinterleaver and RateDe-matching block 450 or 450′, and decoded at Decoder 460 or 460′. Aswill be obvious to one of ordinary skill in the art, these two methodsof interference cancellation may be used in systems with more than twousers.

SUMMARY OF THE INVENTION

Example embodiments provide methods, logical flows, and architecturesdesigned to cancel interference at NodeB receivers. Example embodimentsact on baseband antenna signals, including dedicated physical controland data channels and/or enhanced physical control and data channels,which are processed in time sliced architectures. By cancelinginterference in physical channels, enhanced capacity due to an increasein successful decoding of the physical channels may be achieved.

An example embodiment provides a method of decoding physical channels,comprising, receiving a multi-user baseband antenna signal at areceiver. The multi-user baseband antenna signal including physicalchannel transmissions, including transmissions on physical data channelsand physical control channels. The method further demodulates receivedphysical data channel signal transmission. The demodulating step mayinclude at least despreading and maximal ratio combining multi-pathcomponents of the received baseband antenna signal. Demodulating is alsoperformed on previous physical data channel transmissions ofunsuccessfully decoded users included in a delayed interferencecancelled multi-user baseband antenna signal. The demodulation stepincludes at least despreading and maximal ratio combining of multi-pathcomponents of the delayed multi-user interference cancelled basebandantenna signal.

In another example embodiment, physical control channel transmissionsare demodulated and combined with previous interference cancelledphysical control channel transmissions, similar to the method ofphysical data channel transmissions. The physical control channeltransmissions and the previous interference cancelled physical controlchannel transmissions are demodulated symbol by symbol, each symbolbeing divided into equal time slices where each user is assigned asingle time slice per symbol. The method also includes combining thedemodulated physical data channel transmissions and the demodulatedprevious interference cancelled physical data channel transmissions.

The method may further include error correcting the combined demodulatedtransmissions and decoding the error corrected transmission. Also, theerror correction may include HARQ combining. All steps of the method maybe repeated as new multi-user baseband antenna signals are received. Theuse of the combined transmissions in error correction and decodingincrease the success of decoding previously unsuccessfully decodedusers.

Other example embodiments provide methods of interference cancellation,comprising, receiving a multi-user baseband antenna signal at a receiverincluding physical channel transmissions. The physical data channeltransmissions are demodulated, the demodulation may include the steps ofat least first stage despreading and maximal ratio combining multi-pathcomponents of the received baseband antenna signal. Demodulation mayalso include at least second despreading, deinterleaving, and ratede-matching the first demodulated received physical data channeltransmissions. The method further includes error correcting the receiveddemodulated physical data channel transmissions for each and decodingthe error corrected user transmissions. The error correction may includeHARQ combining and the decoder may be a Turbo decoder. If a transportblock for a user is successfully decoded the transport block isre-encoded and a reconstructed baseband antenna signal is reconstructedfrom the re-encoded user transport block. The user signal reconstructedfrom the transport block may also use multi-path profile and associatedchannel estimates to form a reconstructed baseband antenna signal forthat user, the reconstructed baseband antenna signal is combined withthat of other users and removed from the received baseband antennasignal.

A second multi-user baseband antenna signal may then be received at thereceiver and demodulated in a similar way as discussed above. Theprevious physical data channel transmissions included in the delayedinterference cancelled baseband antenna signal are also demodulated andthese demodulated transmissions are then combined to form an aggregatesignal for each previous user. Following the combining step, theaggregate signal for each user is decoded.

The above example embodiment methods may be repeated as often asdetermined by the number of users that are unsuccessfully decoded and/oras determined by network/system conditions. The physical data channelsmay be enhanced physical data channels. The received multi-user basebandantenna signal may be stored in at least one buffer and the interferencecancelled delayed baseband antenna signal may be stored in a buffer.

Example embodiments also include methods of interference cancellation,including receiving a multi-user baseband antenna signal at a receiver,the multi-user baseband antenna signal including at least physical datachannel transmissions. The method further demodulates the physical datachannel transmissions, which may include at least first stagedespreading and maximal ratio combining multi-path components of thereceived baseband antenna signal. A user symbol energy value isdetermined for at least one user of the multi-users based on thedemodulated user physical data channel transmissions, where if theuser's symbol energy exceeds a threshold, a physical data channel signalfor the at least one user is reconstructed at a chip rate correspondingto the determined user's symbol energy. To cancel interference, thereconstructed physical data channels are removed from the multi-userbaseband antenna signal to form an interference cancelled basebandantenna signal.

The method may further include using the interference cancelled basebandantenna signal plus the user's removed interference for each user whosereconstructed physical data channels were removed from the multi-userbaseband signal, and using the interference cancelled baseband signalfor each user who was not removed from the multi-user baseband antennasignal for further processing by the receiver.

Example embodiments also include methods of interference cancellation,including error correcting a demodulated physical data channeltransmission for a first user at a receiver and decoding the combineduser signal. If the first user's transmission is successfully decoded,the decoded transmission is re-encoded and the interference of there-encoded first user transmission on other users is determined. Thedetermined interference is removed from a second user's transmission.These steps may be repeated for all users who are successfully decoded.The determined interference may be determined symbol interference, andthe error correction may be HARQ combining. Various error correctingprocesses/methods may be chosen, for example, interleaving, ratematching, HARQ combining, Turbo, convolution coding, CRC attachment,etc. The interference determining may use pre-computed crosscorrelations of scrambling and spreading codes or by computing the crosscorrelations on the fly, along with multi-path profiles and channelestimates.

Additional example embodiments include combinations of the variousexample embodiments discussed above to further increase successfuldecoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings. FIGS. 1-9 represent non-limiting, example embodiments asdescribed herein.

FIG. 1 illustrates a conventional wireless communication systemoperating in accordance with UMTS protocols;

FIGS. 2A-2B illustrate example portions of a conventional uplink RFsignal receiver;

FIG. 3 illustrates the conventional concept of signal interference;

FIGS. 4A-4B illustrate conventional methods of interferencecancellation;

FIG. 5 illustrates an interference cancellation method, according toexample embodiments;

FIG. 6A shows a portion of a NodeB receiver and logical flows, accordingto example embodiments;

FIG. 6B illustrates further detail, of block 680 of FIG. 6A;

FIG. 7 illustrates an interference cancellation method, logical flow,and architecture, according to example embodiments;

FIG. 8 illustrates an example interference cancellation receiverarchitecture, logical flow, and method, according to example embodimentsand;

FIG. 9 illustrates an example interference cancellation receiverarchitecture, logical flows, and method for combining FIG. 6 and FIG. 8,according to example embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various example embodiments will now be described more fully withreference to the accompanying drawings in which some example embodimentsare illustrated.

Accordingly, while example embodiments are capable of variousmodifications and alternative forms, embodiments thereof are shown byway of example in the drawings and will herein be described in detail.It should be understood, however, that there is no intent to limitexample embodiments to the particular forms disclosed, but on thecontrary, example embodiments are to cover all modifications,equivalents, and alternatives falling within the scope of the invention.Like numbers refer to like elements throughout the description of thefigures.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items. Theterminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise.

It should also be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which example embodiments belong. Itwill be further understood that terms, e.g., those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Portions of the present invention and corresponding detailed descriptionare presented in terms of software, or algorithms and symbolicrepresentations of operation on data bits within a computer memory.These descriptions and representations are the ones by which those ofordinary skill in the art effectively convey the substance of their workto others of ordinary skill in the art. An algorithm, as the term isused here, and as it is used generally, is conceived to be aself-consistent sequence of steps leading to a desired result. The stepsare those requiring physical manipulations of physical quantities.

Usually, though not necessarily, these quantities take the form ofoptical, electrical, or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise, or as is apparent from the discussion,terms such as “processing” or “computing” or “calculating” or“determining” of “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data represented as physical, electronicquantities within the computer system's registers and memories intoother data similarly represented as physical quantities within thecomputer system memories or registers or other such information storage,transmission or display devices.

Note also that the software implemented aspects of the invention aretypically encoded on some form of program storage medium or implementedover some type of transmission medium. The program storage medium may bemagnetic (e.g., a floppy disk or a hard drive) or optical (e.g., acompact disk read only memory, or “CD ROM”), and may be read only orrandom access. Similarly, the transmission medium may be twisted wirepairs, coaxial cable, optical fiber, or some other suitable transmissionmedium known to the art. The invention is not limited by these aspectsof any given implementation.

As used below the terms base station, base transceiver station (BTS) andNodeB are synonymous and may be used interchangeably to describeequipment that provides data connectivity between a wireless network andone or more UEs. Additionally where used below, the terms user, userequipment (UE), subscriber, mobile station, and remote station aresynonymous and may be used interchangeably to describe a remote user ofwireless resources in a wireless communication network. Also, themethods, logical flows, and architectures described may apply to any andall antennas and sectors. In addition, while the methods, logical flows,and architectures are described using aligned users, non-aligned usersmay be used as well.

As discussed above with regard to FIG. 1, a multi-user environment mayinclude at least a first type of user 110, which may be a higher datarate user such as a UMTS Release 6 user, referred to herein as anenhanced user, and a second type of user 105, which may be a loweruplink data rate user such as a UMTS Release 4/5 user, referred toherein as a legacy user. Enhanced users 110 transmit signals to aserving NodeB 120/122/124 simultaneously over E-DCHs (e.g., E-DPDCHs andE-DPCCHs), DCHs (e.g., DPDCHs and DPCCHs), and HS-DPCCHs. Legacy users105 transmit signals over DCHs, and HS-DPCCHs. As discussed above, theseenhanced and legacy dedicated physical channels may be transmitted overrespective propagation channels, each of which may include multiplepropagation paths.

FIG. 5 illustrates a method of interference cancellation of a physicaldata channel according to an example embodiment of the presentinvention. FIG. 6A illustrates an overview of a modified NodeB receivershown in FIG. 2A. FIG. 6A further includes DPCCH receiver 602 outputtingDPCCH pilots 686 to E-DCH receiver 680 and HSDPA receiver 606 outputtingHS-DPCCH information bits 690 to E-DCH receiver 680. These additionalinputs are used as described below for interference cancellationaccording to example embodiments. Receiver 680 may be located at, forexample, any or all of the NodeBs 120/122/124 shown in FIG. 1. Forexemplary purposes, example embodiments of the present invention will bediscussed with regard to the conventional wireless system shown in FIGS.1-2B. However, it is understood that example embodiments of the presentinvention may be implemented in conjunction with any suitable wirelesstelecommunications network (e.g., UMTS, CDMA2000, etc.).

For purposes of example, FIG. 5 illustrates a first over the airbaseband antenna signal 280 comprising two user signals (signal 280 mayinclude more than two users). In FIG. 5, baseband antenna signal 280includes a transmission for UE A and a first transmission (1st) for UE Bon a physical data channel. Signal 280 is demodulated in step S520 andHARQ combined with previous transmissions, if any, and decoded in stepS530 as shown on the left side of FIG. 5. Step S520 may occur in blocks210 and 230, for the E-DPDCHs and at block 200 for the E-DPCCHs, aspreviously described in FIG. 2B. Step S530 occurs at SSD and HARQ blocks250, 260, and Dec block 270, also previously described for the E-DPDCHsin FIG. 2B. Following successful decoding of user A as shown in FIG. 5,user A's signal is reconstructed and removed from first signal 280 toproduce an interference cancelled baseband antenna signal compromisinguser B's transmission (1^(st)), in this example, (shown as UE B 1^(st)′)in step S540. User B's transmission included in the interferencecancelled baseband antenna signal is also referred to as a previoustransmission for user B (in the future) and is stored in ICB block 510,which is a “clean” buffer in step S545. The stored transmission has hadsome interference removed and in this example is equivalent to a delayedinterference cancelled baseband antenna signal. The delayed interferencecancelled baseband antenna signal may include more than one user, andmore than one user's transmission may be removed from the receivedbaseband antenna signal 280 to form the delayed interference cancelledbaseband antenna signal.

As shown on the right side of FIG. 5, a second over the air basebandantenna signal 280′ is received, at a later time. Second signal 280′includes a retransmission for UE B and an initial transmission for UE A.Essentially the same demodulating process S520 is performed on thesecond signal 280′ as discussed above. However, prior to the secondsignal 280′ being HARQ combined at step S530, the delayed interferencecancelled baseband antenna signal, in this example, is equivalent to UEB 1^(st) and is demodulated in step S525. In step S527, the demodulateddelayed interference cancelled baseband antenna signal UE B 1^(st) andthe demodulated second signal 280′ are combined in HARQ combiner 260 anddecoded in DEC 270. The delayed interference cancelled baseband antennasignal containing UE B 1^(st) has had interference removed, andtherefore successful decoding of UE B's transport blocks increases. Atransport block is a block of data sent over one TTI and a transmissionis an instance of a block of data sent from a transmitter to a receiver.

FIG. 5 also shows that user B is successfully decoded and user A is notin step S530. Therefore, in step S550, user B's transmission isreconstructed and removed from second baseband antenna signal 280′ toproduce an interference cancelled baseband antenna signal UE A′, whichcontains user's A transmission, also referred to as a previoustransmission for user A (in the future). The interference cancelledbaseband signal UE A′ is stored in ICB block 510 in step S555. Theinterference cancellation process shown in FIG. 5 may be performed formore users and/or as necessary to ensure successful decoding of users'transmissions.

The method shown in FIG. 5 and the additional inputs shown in FIG. 6Aare further described with reference to FIG. 6B. FIG. 6B includes all ofthe blocks of FIG. 2B and additional blocks, Re-ENC 630, Re-ENC-E-DPCCH670, CRSR 640, TRSR 650, IS 660, ICB 510, CEB 600, E-DPCCH_RR_PT 625,and RR-FSD-PT 620. The blocks and their corresponding function shown inFIG. 2B have been described and thus the focus will be on the new blocksand their functions.

In FIG. 6B, the baseband antenna signal 280 is received at block 510,block 200, and block 210. ICB block 510 is an interference cancelledbuffer, also referred to as a “clean buffer” in FIG. 5. Channelestimates 290 are received at block 600 and block 200 and 210. CEB block600 is a channel estimation buffer. ICB block 510 and CEB block 600, forexample, may be external memories or embedded memories, similar to HARQB230 discussed above. As shown in FIG. 5, ICB block 510 may storeincoming baseband antenna signals and interference cancelled basebandantenna signals, while CEB block 600 may store channel estimates andrake finger delay information.

As shown in FIG. 6B, each users' physical data channel transmissions (ofthe same transport block) that are successfully decoded are re-encodedin Re-ENC block 630 and the corresponding control channels arere-encoded in RE-ENC-E-DPCCH block 670. The re-encoded physical datasignals are reconstructed at TRSR block 650 as described with respect tosteps S540 and S550 of FIG. 5. Similarly, the re-encoded physicalcontrol signals are reconstructed at CRSR block 640 during step S540 ofFIG. 5. The output of CRSR block 640 and TRSR block 650 are combined toform a reconstructed baseband antenna signal at IS block 660, includingsignals from all successfully decoded users that were transmitted at thesame time. Therefore the reconstructed baseband signal may include oneuser, a portion of the users, or almost all the users based on how manyusers were successfully decoded. As shown in FIG. 5, the reconstructedbaseband antenna signal first included UE A's successfully decodedtransmissions and then UE B's successfully decoded transmissions in thesecond reconstructed baseband antenna signal.

Also at IS block 660 during step S540, the reconstructed basebandantenna signal is subtracted from first baseband antenna signal 280,which was previously stored in ICB block 510. The result is the delayedinterference cancelled baseband antenna signal discussed in FIG. 5 to beused with users who were not successfully decoded, also referred to asthe previous transmission for these users.

The reconstructed baseband signal may include every successfully decodeduser, and the subtraction or removal of the reconstructed basebandsignal removes these decoded users in a batch process, as compared toremoving the users one by one, sequentially. For example, the users thatare transmitted at the same time and successfully decoded, have theresignals reconstructed in a time-sliced manner, e.g., by symbols. Thereconstructed signals for all users are then added together by symbolsand subtracted (as one group) from the received baseband antenna signal.The delayed interference cancelled baseband antenna signal is thenstored in ICB 510 as described in FIG. 5 in step S545.

The interference cancellation method continues as described in FIG. 5 byreceiving a second baseband antenna signal 280′. The process for secondreconstructed baseband antenna signal 280′ is the same as for firstbaseband antenna signal 280, except prior to HARQ combining anddecoding, the delayed interference cancelled baseband antenna signalcontaining the previous transmissions for the unsuccessfully decodedusers (UE B 1^(st)′ in FIG. 5) is also demodulated in step S525. FIG. 6Bincludes the following blocks that demodulate the delayed interferencecancelled baseband antenna signal, similarly named blocks function inthe same way as previous described. In FIG. 6B, E-DPCCH-RR-PT 625functions the same as E-DPCCH-RR-CT but on the previous transmission(PT) as compared to the current transmission (CT), RR-FSD-PT block 620functions the same as RR-FSD-CT, HARQB block 230 and SSD block 250 arethe same.

The demodulated transmissions for the same user are combined in HARQcombiner block 260 and decoded by DEC 270 in step S530. As shown in FIG.5, an example may include UE A's signal not being successfully decoded,whereas UE B's signal is successfully decoded in step S530. In thisexample, UE B's signal is then reconstructed and removed from the secondsignal 280′ in step S550 producing a delayed interference cancelledbaseband antenna signal containing the previous transmissioncorresponding to UE A, which is stored in ICB 510 in step S555.

The above described interference cancellation processes may be repeatedas often as necessary and for and with as many users as necessary. Bycanceling the interference in a received baseband antenna signal andusing the formed delayed interference cancelled baseband antenna signalin combination with a new received baseband antenna signal, successfuldecoding of user's retransmissions, will increase. It is noted that foreach successfully decoded transport block, the previous usertransmissions may all be interference cancelled or a portion of the usertransmissions may be interference cancelled.

FIG. 7 illustrates another method of interference cancellation accordingto example embodiments. The blocks illustrated in FIG. 7 are the sameshown in, for example, a portion of FIG. 2B, but block 750 is addedprior to block 710 (modified block 210) and block 700 (modified block200). As shown in FIG. 7, a multi-user baseband antenna signal 280 isinput to block 750 including physical data channel transmissions, e.g.,E-DPDCH. In step S800, the received multi-user baseband antenna signalis demodulated, for example, at least first stage despreading and MRCingare performed. The demodulation is performed symbol by symbol and instep S810, a user symbol energy value is determined for each user'ssymbol. The determined user symbol energy value is compared to athreshold in step S810 and users with a determined user symbol energyvalue exceeding the threshold are reconstructed using the chip rate atthe user's symbol. The threshold user symbol energy value may be set bythe service/network provider in view of network parameters and/or systemrequirements, and propagation environments. In step S820, allreconstructed user signals are removed and/or subtracted from basebandantenna signal 280 forming an interference cancelled baseband antennasignal 780.

In steps S840 and S850, for each user, either interference cancelledsignal 780 combined with the specific user's reconstructed user signal,or the interference cancelled signal 780 is input to blocks 710 and 700,respectively, to continue processing at the receiver. For example, theinterference cancelled signal 780 may be input (S840 and S850) to blocks710 and 700 for each user whose determined user symbol energy value didnot exceed the threshold and/or was not subtracted, whereas acombination of the interference cancelled signal 780 and the user'sreconstructed user signal may be input (S840 and S850) to block 710 and700 for each user whose determined symbol energy value did exceed thethreshold and/or was subtracted.

FIG. 8 illustrates another method of interference cancellation accordingto example embodiments. The blocks illustrated in FIG. 8 are the same asshown in, for example, FIG. 2B, but blocks 910 and 920 are substitutedfor block 260, and block 630 (as shown in FIG. 6B) has been added. Themethod and architecture shown in FIG. 8 use a re-encoded user physicaldata channel transmission to determine the interference effect of there-encoded user on another user's symbols transmitted at the same time,and to then cancel the determined interference effect from the anotheruser's symbols being decoded.

As discussed with reference to FIGS. 5 and 6A-B, a user's physical datachannel transmission is re-encoded at Re-ENC 630 if the user's physicaldata channel transmission was successfully decoded at DEC block 270. Asdiscussed before, error correction may refer to, for example,interleaving, rate matching, HARQ combining, etc., and decoding mayrefer to Turbo decoding as well as other decoding chain functions. InFIG. 8, the re-encoded user's physical data channel transmission isinput into block 920, where the re-encoded user's interference on thenext user is determined. This can be for the current transmission aswell as for previous transmissions. The next user may include each userwhose physical data channel transmission was transmitted at the sametime as the re-encoded user's. The determined interference may includethe interference from the re-encoded user's symbols. The determinedinterference is then input into block 910. In block 910 the next user'spost despread physical data channel transmissions are HARQ combined(although various forms of error correction may be used as discussedabove) and the determined interference is removed. This process may beadditive, for example, successfully decoded users' determinedinterference could be combined and removed from the next user'stransmissions. However, any unsuccessfully decoded users would obviouslynot be included in the determined interference as they would not bere-encoded.

The determined interference for a user may be determined by using thecross correlation between the user's and the next user's scramblingcodes for all symbols and all possible symbol offsets. For example thecross correlation may be stored in a look-up table or computed on the“fly” using multi-path profile and channel estimates.

The example embodiment methods and architectures discussed above may becombined in various ways to further enhance interference cancellationand successful decoding of received baseband signals. For example, FIG.9 illustrates a combination of the example embodiment methods andarchitecture shown in FIGS. 5, 6B, and 8.

In FIG. 9, the HARQ block 260 of FIG. 6B is replaced with previouslydescribed blocks 910 and 920 and the Re-ENC block 630 inputs to block920 as well as block 650. Therefore, the baseband antenna signalprocessing includes removing determined symbol interference of one useron other users transmitted in the same baseband signal 280 as describedin FIG. 8; and storing a delayed interference cancelled baseband signalto process and combine with a second baseband antenna signal 280′ asdescribed in FIGS. 5 and 6B.

Other combinations are also possible. For example, block 750 of FIG. 7may be added to the architecture of FIG. 6B before blocks 210 and 200,or before blocks 210, 200, 620, and 625. Therefore, the method describedin FIGS. 5 and 6A-B would use either an interference cancelled basebandsignal 780 combined with the user's reconstructed signal, or theinterference cancelled baseband signal 780 (which is a function of 280)as inputs to blocks 210 and 200 as indicated in FIG. 7; or a furtherinterference cancelled delayed interference cancelled baseband signal(which is a function of the delayed interference cancelled basebandsignal stored in ICB 510), or the further interference cancelled delayedinterference cancelled baseband signal combined with the user'sreconstructed signal as inputs to blocks 610 and 620.

Additionally, the architectures and methods of FIGS. 7 and 8 may becombined. For example, block 750 may be added before blocks 200 and 210of FIG. 8. However, to use both types of interference cancellations onone baseband antenna signal 280, a first subset of the transmittedusers' signals would be interference cancelled as a result of processingin block 780 and a second subset of the transmitted users' signals wouldbe interference cancelled as a result of processing in blocks 920 and910. The first subset of users and the second subset of users beingexclusive of each other. Also the architectures and methods of FIGS. 5,6A-B, 7, and 8 may all be combined. For example, FIG. 7 may be added toFIG. 9 as described with reference to adding FIG. 7 to FIGS. 5 and 6A-Band FIG. 7 to FIG. 8. The same rules regarding the subset of users wouldapply to this combination as described with reference to combining FIGS.7 and 8, but any subset, including users in both identified subsetscould be interference cancelled through the method described in FIGS. 5and 6A-B.

One or more example embodiments of the present invention provideimproved system performance, for example, reduced interference betweenusers, increased cell capacity, increased data throughput, etc.

Example embodiments of the present invention being thus described, itwill be obvious that the same may be varied in many ways. Suchvariations are not to be regarded as a departure from the invention, andall such modifications are intended to be included within the scope ofthe invention.

We claim:
 1. A method of decoding physical channels, comprising:receiving a multi-user baseband antenna signal at a receiver, themulti-user baseband antenna signal including received physical channeltransmissions; demodulating received physical data channel transmissionssymbol by symbol; demodulating previous interference cancelled physicaldata channel transmissions of a delayed multi-user interferencecancelled baseband antenna signal, symbol by symbol; and combining thedemodulated received physical data channel transmissions with thedemodulated previous interference cancelled physical data channeltransmissions.
 2. The method of claim 1, further comprising: errorcorrecting the combined demodulated transmissions; and decoding theerror corrected transmissions.
 3. The method of claim 1, wherein eachsymbol time period for the received physical data channel transmissionsis divided into equal time slices and each user is assigned a singletime slice per symbol.
 4. The method of claim 1, wherein each symboltime period for the previous interference cancelled physical datachannel transmissions is divided into equal time slices based on thenumber of users, and each user is assigned a single time slice persymbol.
 5. The method of claim 1, wherein the method increases thedecoding success for previously unsuccessfully decoded users.
 6. Themethod of claim 1, wherein the receiving, demodulation, and combiningsteps are repeated for newly received multi-user baseband antennasignals.
 7. The method of claim 1, wherein the step of demodulating thereceived physical data channel transmissions, further includes: at leastpartially despreading and maximal ratio combining the multi-pathcomponents of the received multi-user baseband antenna signal.
 8. Themethod of claim 1, wherein the step of demodulating the previousinterference cancelled physical data channel transmissions, furtherincludes: at least partially despreading and maximal ratio combining themulti-paths components of the delayed multi-user interference cancelledbaseband antenna signal.
 9. The method of claim 1, wherein the physicaldata channels are enhanced dedicated physical data channels (E-DPDCHs).10. The method of claim 1, further comprising: demodulating receivedphysical control channel transmission; demodulating previousinterference cancelled physical control channel transmissions of thedelayed multi-user interference cancelled baseband antenna signal; andcombining the demodulated received physical control channeltransmissions with the demodulated previous interference cancelledphysical control channel transmissions.
 11. The method of claim 10,wherein the step of demodulating the received physical control channeltransmissions, further includes: at least despreading and maximal ratiocombining the multi-path components of the received multi-user basebandantenna signal.
 12. The method of claim 10, wherein the step ofdemodulating the previous interference cancelled physical controlchannel transmissions, further includes: at least despreading andmaximal ratio combining the multi-paths components of the delayedmulti-user interference cancelled baseband antenna signal.
 13. Themethod of claim 10, wherein the physical control channels are anenhanced dedicated physical control channels (E-DPCCHs).
 14. The methodof claim 1, wherein the error correcting step further includes, HybridAutomatic Repeat Request (HARQ) combining multiple physical data channeltransmissions of a same transport block; and the decoding steps furtherincludes, decoding the output of the HARQ combiner.
 15. The method ofclaim 1, wherein the receiving step further includes receiving channelestimates and multi-path delay profiles to assist in the reconstructionof the signal.
 16. The method of claim 1, further comprising: receivinga multi-user baseband antenna signal at a receiver, the multi-userbaseband antenna signal including physical channel transmissions;demodulating physical data channel transmissions; determining a usersymbol energy value for each of the multiple users; removing areconstructed chip data rate signal for each user with a determinedsymbol energy value exceeding a threshold from the multi-user basebandantenna signal to form an interference cancelled baseband antennasignal; substituting the received multi-user baseband antenna signalwith the interference cancelled baseband antenna signal.
 17. The methodof claim 16, further comprising; error correcting the combineddemodulated physical data channel transmission for a first user;decoding the error corrected first user transmission; re-encoding thesuccessfully decoded first user transmission; determining aninterference of the first user on other users; and removing thedetermined interference from the demodulated physical data channeltransmission for a second user, forming an interference cancelledcombined demodulated physical data channel transmission for the seconduser.